1. Field of the Invention
The present invention relates to a sensor and a set of sensors for use, for example, in measurement of a liquid sample of an organism.
2. Description of the Prior Art
Conventionally, a disposable sensor has been used for general purposes in the field of clinical tests such as biochemical analysis (e.g., Japanese Laid-Open Patent Publication No. 4-188065 and Japanese Patent Publication No. 6-58338). A disposable sensor does not need cleaning after measurement, so that it is suitable for personal use. In particular, a sensor having a capillary passage easily used with a liquid sample such as blood is advantageous for self-monitoring such as self-measurement of blood glucose. Such a sensor can be categorized into two types, i.e., electrochemical type and optical type, which are different from each other in the detecting means.
An electrochemical sensor is provided with, for example, electrodes arranged on a rectangular substrate and a passage through which a sample flows. An end of the passage constitutes an inlet for a sample. A reagent that is changed electrochemically when it reacts with the sample is generally placed on the electrodes. When a sample such as blood is contacted with the sample inlet, the sample is drawn through the passage into an electrode part (analyzing part) by capillary phenomenon, and the sample reacts with the reagent. A component of the sample can be analyzed in the following manner. This sensor is positioned in a measuring device, a sample is supplied, and a voltage is applied to the electrodes. Then, a reaction with the reagent is detected by the electrodes as an electrochemical change.
In an optical sensor, instead of the electrodes and the reagent that effects an electrochemical change, a reagent that effects an optical change when it reacts with a sample is placed on the substrate. A part of the sensor is externally observable by being transparent so that the optical change is detected outside the sensor. Other than that, the optical sensor has the same configuration as that of the electrochemical sensor. The optical change of the reagent is measured by visual observation, a spectrophotometer, a reflectometer or the like. In this manner, a component of the sample is analyzed.
High precision in measurement is required for such a sensor. Therefore, the sensor is prevented from being in contact with the outside, for example, by being contained in a can or closely packaged with an aluminum foil seal one by one, in order to ensure temporal stability of a reagent containing enzyme or to prevent a substance that could interfere with measurement from entering the sensor. However, the containment in a can or the packaging with seals increases the number of steps for production of the sensor, thus leading to high cost. In addition, the containment or the packaging deteriorates the operability of the sensor when it is used.